Advertise WebP read support via .desktop files

This resolves issue #1

Signed-off-by: Alex Kent Hajnal <software@alephnull.net>
(cherry picked from commit 9cb3d5b8ca)

src/desktopfiles/gwenview.desktop

@@ -11,5 +11,5 @@ Icon=gwenview
 Exec=gwenview %u -caption "%c" %i %m
 Terminal=false
 Categories=Qt;TDE;Graphics;
-MimeType=image/gif;image/x-xpm;image/x-xbm;image/jpeg;image/x-pcx;image/x-bmp;image/png;image/x-ico;image/x-portable-bitmap;image/x-portable-pixmap;image/x-portable-greymap;image/tiff;image/x-targa;image/svg+xml;
+MimeType=image/gif;image/x-xpm;image/x-xbm;image/jpeg;image/x-pcx;image/x-bmp;image/png;image/webp;image/x-ico;image/x-portable-bitmap;image/x-portable-pixmap;image/x-portable-greymap;image/tiff;image/x-targa;image/svg+xml;
 X-DocPath=gwenview/index.html

src/gvimagepart/gvimagepart.desktop

@@ -2,7 +2,7 @@
 Type=Service
 Name=Gwenview Image Viewer
 Icon=gwenview
-MimeType=image/gif;image/jpeg;image/png;image/x-bmp;image/x-eps;image/x-ico;image/x-krl;image/x-portable-bitmap;image/x-portable-pixmap;image/x-xbm;image/x-xpm
+MimeType=image/gif;image/jpeg;image/png;image/webp;image/x-bmp;image/x-eps;image/x-ico;image/x-krl;image/x-portable-bitmap;image/x-portable-pixmap;image/x-xbm;image/x-xpm
 X-TDE-ServiceTypes=KParts/ReadOnlyPart
 X-TDE-Library=libgvimagepart
 X-TDE-InitialPreference=5